Real-time display systems based on spatial light modulators (SLMs) are increasingly being used as an alternative to display systems using cathode ray tubes (CRTs). SIM systems provide high resolution displays without the bulk and power consumption of a CRT system.
Digital micromirror devices (DMDs) are a type of SLM, and may be used in projection display applications. A DMD has an array of micro-mechanical pixel elements, each having a mirror and a memory cell. Each pixel element is individually addressable by electronic data. Depending on the state of its addressing signal, each mirror element is tilted so that it either does or does not reflect light to the image plane. Other SIMs operate on similar principles, with pixel elements that emit or reflect light simultaneously with other pixel elements, such that a complete image frame is generated by addressing pixel elements rather than by scanning them.
For processing data in an SIM-based systems, as is the case with other digital image processing systems, the processor operates on pixel data. Interlaced data is arranged pixel-by-pixel, row-by-row, and field-by-field. Scan conversion techniques are used to generate frames from fields. In a standard television system, for example, images are transmitted at 30 frames per second, and each frame lasts for approximately 33.3 milliseconds. Non-interlaced data is already arranged as frames.
Processing tasks such as colorspace conversion and scaling, as well as scan conversion, are performed on the pixel data.
However, in an SLM-based system, the SLM must receive the data in "bit-planes". In other words, pixel data must be reformatted into bit-level data so that each pixel element can be "on" or "off" a length of time corresponding to the value of its pixel data. Various modulation schemes determine how long each pixel is on or off, and permit greyscale and color images to be displayed. A bit-plane represents all bits of all pixels having the same digital weight. For pixels having an n-bit resolution, there are n bit-planes per display frame.
SLM-based systems use a "display memory" to provide bit-planes of data to the SLM. Existing display memories are "double buffered", so that they can store data for a current frame while data for a next frame is being written in. This permits each frame of data to be read out of memory and displayed on the SIM during its own frame period. Many display memories operating in this double-buffered mode require a capacity of two frames of data. A variation of double-buffering is dynamically allocating memory space so as to reduce the required capacity. U.S. Pat. Ser. No. 07/755.883, entitled "Dynamic Memory Allocation For Frame Buffer for Spatial Light Modulator", assigned to Texas Instruments Incorporated, discusses these methods of using a display memory.